SIM (subscriber identity module) cards are smart cards that are commonly found in mobile phones. Indeed, SIM cards are an essential part of almost all mobile phones operating in a mobile cellular communications network such as GSM or UMTS (Universal Mobile Telecommunications System). In a third generation (3G) networks such as UMTS, the SIM card is capable of holding several applications including the standard SIM application that is used primarily to authenticate the mobile subscriber in the 3G network.
In the past, SIM based authentication in GSM and 3G has always been linked with the mobile cellular network itself. For example, under 3G, SIM based authentication is linked to the home subscriber server (HSS) within the core mobile cellular network. The HSS stores subscriber and authentication information associated with the SIM, and authenticates the SIM, and consequently the mobile phone, by verifying the information stored on the SIM. This is done using a challenge response technique to verify that a shared secret key held securely at both the HSS and on the SIM are the same. Once authenticated, further authentication keys can be generated by the HSS and the SIM so that communications between the HSS, and other entities in the mobile cellular network appropriately authorised by the HSS such as application servers, and the device containing the SIM can be made securely.
However, there are no provisions in existing systems to initiate authentication from the mobile device or SIM itself, and to direct the authentication to other local entities or other devices directly rather than through the HSS or the mobile cellular network.
In fact, there are no provisions in existing systems to use a SIM in a more active way, and specifically ones that utilise the tamper-resistance nature of the SIM as well as its authentication capability in the local environment, such as in a local Wi-Fi network. Existing solutions such as the Generic Authentication Architecture (GAA) under the 3G specifications or the Extensible Authentication Protocol for SIM (EAP-SIM) capitalise on the existing asymmetric relationship between the HSS and the SIM and require the involvement of the network operator in every authentication process and therefore require a connection to the operator's equipment during the actual authentication. Such solutions are not suitable for the local environment where the connection to operator's equipment cannot be always guaranteed or in situations where the operator does not want to be involved as a primary authentication resource once the local network is arranged.